The present invention is directed to a tracking device, and, more particularly, to a device for tracking an individual or an object, having improved reliability.
Personal tracking devices have been found to be extremely useful in locating lost objects and, more importantly, missing persons. Such tracking devices typically use a network of Global Positioning Satellites (GPS) in low earth orbit that broadcast precise timing signals from on-board atomic clocks. Using triangulation formulas, a device that picks up signals from several satellites simultaneously can determine its position in global coordinates, namely latitude and longitude.
A device with a GPS receiver has a 24 hour a day line-of-sight view to a sufficient number of satellites at any spot on the earth such that a person with a GPS receiver is able to determine their own longitude and latitude to within several meters, as well as their elevation. However, the fact that an individual knows their own position in longitude and latitude does not help others find them without extremely precise topographical or geophysical maps, which also show longitude and latitude. Furthermore, the degree of precision in position determination is then only accurate to the resolution of the maps on hand and to the degree of accuracy provided by the GPS hardware.
Dead-reckoning is well known as a method of guiding ships, whereby the known velocity and direction of travel of a ship from a known position is used to calculate the current position of the ship. However, the further the ship moves away from the known position, the less accurate the dead-reckoning position becomes. Adverse weather conditions can also erode the accuracy of navigation by dead-reckoning.
With a GPS receiver and a very accurate map, a ship can be guided with a suitable degree of precision. However, due to the possibility of military uses of the GPS system by adversaries, the GPS timing signals broadcast by the satellite network for commercial use are intentionally made less accurate than GPS signals that are encoded for military uses. These timing and position errors are known as Selective Availability (SA), and reduce the accuracy of civilian users of the GPS signals. This reduced accuracy may not be suitable for tracking objects and individuals, and, therefore, can erase the benefits of the GPS technology.
U.S. Pat. No. 5,781,150 to Norris discloses a tracking device having an RF transmitter and an RF receiver, each of which have a built-in GPS receiver. The transmitter sends its GPS position via an RF signal to the receiver, which in turn calculates the position of the transmitter relative to that of the receiver. The receiver then displays range and bearing information regarding the transmitter""s location with respect to the receiver.
Norris is limited in that such a device provides no information regarding the reliability of the RF signal sent. Additional problems are encountered when using such a GPS system in a man-overboard situation. A radio transmitter that relies on xe2x80x9cline of sightxe2x80x9d from its antenna to a receiver for reliable transmission is subject to potential signal loss when operated at the surface of the sea. Waves can obscure the direct line of sight of the antenna, and may tend to submerge the transmitting antenna. This is particularly true for a transmitter that is worn or carried by a person floating on the surface of the water. Transmission of a signal, such as an RF signal, can be obscured by waves, and the transmitter can be subject to immersion, resulting in wasted energy and signal loss. This results in shortened transmitter battery life and decreased transmission reliability.
It is an object of the present invention to provide a tracking device that reduces or wholly overcomes some or all of the difficulties inherent in prior known devices. Particular objects and advantages of the invention will be apparent to those skilled in the art, that is, those who are knowledgeable or experienced in this field of technology, in view of the following disclosure of the invention and detailed description of preferred embodiments.
The principles of the invention may be used to advantage to provide a tracking device for locating lost individuals or objects that can increase the chances that a signal sent by a transmitter of the lost object is received by a device tracking the lost object. Additional embodiments of the present invention can provide an increased level of confidence that the location indicated for the individual or object is accurate.
In accordance with a first aspect, a tracking system includes a target unit having a GPS receiver, a signal transmitter to send a signal indicating a position of the target unit, and a processor to calculate an optimal time interval for transmission of the signal. A locating unit has a GPS signal receiver, a compass to provide a reference direction of the locating unit, a signal receiver to receive the signal sent by the transmitter of the target unit, a processor to calculate a range and bearing from the locating unit to the target unit, and an indicator to display the range and bearing.
In accordance with a second aspect, a tracking system includes a target unit having a GPS receiver and a signal transmitter to send a signal indicating a position of the target unit. A locating unit has a GPS signal receiver and a compass to provide a reference direction of the locating unit. A signal receiver receives the signal sent by the transmitter of the target unit. A processor calculates a range and bearing from the locating unit to the target unit and a confidence level to indicate a reliability of the signal sent by the target unit. An indicator displays the range, bearing and confidence level.
In accordance with another aspect, a system to transmit the location of an object or individual associated with the system includes a GPS receiver to determine a position of a device. A signal transmitter sends a signal indicating the position of the device. A processor calculates an optimal time interval for transmission of the signal.
In accordance with yet another aspect, a tracking system to track the location of an object in water includes a target unit having a GPS receiver to determine a position of the target unit. A sensor detects motion of the target unit, and a processor calculates when the target unit is proximate a crest of a wave. A signal transmitter sends a signal indicating the position of the target unit when the target unit is proximate the crest of a wave. A locating unit has a GPS signal receiver and a compass to provide a reference direction of the locating unit. A signal receiver receives the signal sent by the transmitter of the target unit. A processor in the locating unit calculates a range and bearing from the locating unit to the target unit. An indicator displays the range and bearing from the locating unit to the target unit.
In accordance with a further aspect, a method of tracking a target unit from a locating unit includes the steps of receiving a GPS signal at a target unit to determine a location of the target unit, receiving a GPS signal at a locating unit tracking the target unit to determine a location of the locating unit, calculating an optimal time interval for transmission of a signal from the target unit to the locating unit, where the signal includes the GPS location of the target unit, transmitting the signal from the target unit to the locating unit during the optimal time interval, and calculating a range and bearing from the locating unit to the target unit.
In accordance with yet a further aspect, a tracking system includes a tracking unit having a GPS receiver and a signal transmitter to send a signal including a position of the tracking unit. A signal receiver is configured to receive a signal sent by a transmitter of at least another tracking unit. A processor is configured to calculate a range and bearing from the tracking unit to at least another tracking unit and a confidence level attributed to a signal sent by at least another tracking unit. A compass provides a reference direction of the tracking unit, and an indicator is configured to display the range and bearing to at least another tracking unit.
From the foregoing disclosure, it will be readily apparent to those skilled in the art, that is, those who are knowledgeable or experienced in this area of technology, that the present invention provides a significant advance. Preferred embodiments of the tracking device of the present invention can provide increased reliability of signal transmission from a transmitter to a receiver, and increased confidence in the accuracy of the signal being sent. These and additional features and advantages of the invention disclosed here will be further understood from the following detailed disclosure of preferred embodiments.